In the patent world, claim scope depends on the meaning given to the individual words in the claim. If the meaning of a word in the claim is not clear, the claim may be attacked as invalid under the indefiniteness standard. Is a claim indefinite if the claim contains a term that is used by the patentee to refer to a specific compound in one part of the specification and to a broader class of related compounds in another part of the specification? If the claim contains a term that is admitted to have different meanings depending on the context in which the term is used? According to a recent ruling by the Federal Circuit, the answer to both questions is no.

35 U.S.C. § 112, ¶ 2, requires that a patent specification “conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.” Under the Supreme Court’s Nautilus ruling, a claim is invalid for indefiniteness “if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention.”

In Eli Lilly and Company v. Teva Parenteral Medicines, Inc., the issue of indefiniteness turned on the interpretation of the claim term “vitamin B12.” In this case, it was undisputed by the parties that the term “vitamin B12” as used in the specification can refer to either cyanocobalamin (a synthetic form of vitamin B12) specifically or, more broadly, to a class of compounds including pharmaceutical derivatives of cyanocobalamin. The patent defined vitamin B12 to mean “vitamin B12 and its pharmaceutical derivatives,” and that “[p]referably the term refers to vitamin B12, cobalamin, and chlorocobalamin. The parties also agreed that the term “vitamin B12” was used both ways in the specification.

Given these facts, one might think the claims were indefinite under the Nautilus standard. However, the CAFC determined that the claims were not indefinite in the context of the claims (which required administration to a patient), as one of ordinary skill in the art would understand that “vitamin B12” referred specifically to cyanocobalamin in the realm of medical treatment, thereby providing “reasonable certainty” as required under Nautilus.

Teva argued that because the claim term was used both ways in the specification, it was impossible to tell which meaning to use to interpret the scope of the claim with “reasonable certainty.” Lilly countered that the entire claim had to be considered in the indefiniteness inquiry and that since the claim specified administering “a vitamin B12 supplement to a patient,” one of ordinary skill in the art would know that the term referred to cyanocobalamin (which is the form used for human administration). Lilly supported this argument with expert testimony (which was not refuted, and in some ways confirmed, by Teva’s expert).

Understandings that lie outside the patent documents about the meaning of terms to one of skill in the art or the science or state of the knowledge of one of skill in the art are factual issues.

Importantly, the CAFC placed significant weight on the District Court’s use of the expert testimony on the issue and concluded that it found no clear error in the District Court’s conclusion that “vitamin” B12, when used to refer to vitamin B12 supplementation in a medical context, refers to cyanocobalamin.” The court distinguished Teva v. Sandoz on the grounds that the claim term at issue in that case did “not have a plain meaning to one of skill in the art that could be determined from context,” noting the expert admitted that the claim term had “no default meaning” (in contrast to the facts in the present case). In Teva v. Sandoz, the CAFC gave deference to the District Court’s subsidiary factual findings under the clear error standard set forth by the Supreme Court, but reviewed the application of the subsidiary factual findings as applied to the ultimate legal determination of indefiniteness de novo (without deference to the District Court). Because the expert testimony failed to provide reasonable certainty as to the meaning of the claim term, the CAFC found the claims indefinite, reversing the District Court.

The court also considered claim differentiation as supporting a clear meaning for “vitamin B12.” Claim 1 listed both “vitamin B12” and cyanocobalamin (the asserted definition of “vitamin B12”) in claim 1 as suitable agents for use in the method (along with several other vitamin B12 derivatives). Claim 2 limited the agent to “vitamin B12” alone. The CAFC reasoned that since claim 2 specifically referred to “vitamin B12” alone, reading vitamin B12 as referring to a class of compounds would make claim 2 the same scope as claim 1. The court dismissed claim redundancy considerations, based on part on the prosecution history, having no issue with the claim 1 reciting cyanocobalamin twice in the claim.

This case illustrates the importance of expert testimony when fighting an indefiniteness challenge. It is critical that when expert testimony is presented regarding the meaning of a claim term, the testimony address the meaning of the term in the context of the claims to provide the public with reasonable certainty as to the meaning of the claim term in the context of the claims. If successful, the CAFC will have less flexibility in reversing factual determinations made by a District Court based on expert testimony.